Composite wooden panel



Feb. 8, 1966 B. s. BRYANT 3,234,074

COMPOSITE WOODEN PANEL Filed Jan. 14, 1963 2 Sheets-Sheet 1 HARDBOARD BEN S. BRYANT INVENTOR.

g QM 51kt ATTORNEYS B. S. BRYANT Feb. 8, 1966 COMPOSITE WOODEN PANEL 2 Sheets-Sheet 2 Filed Jan. 14, 1963 LUMBER WOOD VENEER PLYWOOD Fl h BEN S. BRYANT A TTORNE YS United States Patent F 3,234,074 COMPOSITE WOODEN PANEL Ben S. Bryant, Seattle, W3Sh., assignor to Weyerliaeuser Company, Tacoma, Wash, a corporation of Washington Filed Jan. 14, 1963, Ser. No. 251,161 6 Claims. (Cl. 161-36) This invention relates to a new and useful concept in a prefabricated structural wooden building panel and the method for its making, and more particularly to a prefabricated structural building panel which can utilize lower grade wood products than have heretofore been employed in the prefabricated wooden panel industry.

In recent years, the building and construction industry has moved increasingly toward the broad scale use of prefabricated building components. This trend has been stimulated by the high cost of raw materials together with the ever increasing high cost of the labor required to manufacture, erect and finish the various building products.

One of the newest classes of prefabricated building components are those which combine plywood and lumber in sucha way as to take fullest advantage of the structural characteristics of each. The resulting products have the labor-saving advantages of other prefabricated components of wood with the added advantage of minimum weight for the strength characteristics needed. Stress-skin panels, which are sandwiches that may be made with plywood surfaces and spaced lumber cores, are typical examples of such prefabricated components. They are used as roof panels and wall panels for homes, industrial, and farm buildings, small apartment buildings, schools and stores.

For most uses, insulation must be incorporated in the hollow portion of the sandwich unless the core itself possesses insulating characteristics, such as would be the case where a non-flammable material was used in the sandwich, .as, for instance, plastic foam material or asbestos.

Perhaps the single greatest limitation of the stress-skin panel is its'inherent lack of fire resistance. When in place in a building, as, for example, in a roof panel, the stresses caused by the roof loads which tend to bend it are concentrated in the outer plywood skins. In the event of fire, if the outer /8 inch of veneer is seriously damaged the structural integrity of the entire panel is lost. While it is possible to pressure treat the plywood with fire retardant compositions so that combusion will not be supported, nevertheless the exposed thin surface of the panel is still vulnerable to damage by fire through charring.

Another problem encountered is that in providing fire resistance to a stress-skin panel, as by the application of light-weight plaster to the ceiling side thereof, the builder incurs a considerable added expense. In fact, such treatment of a panel amounts to more than half the cost of the panel itself.

Another limitation of prefabricated roof panels that are presently known is the fact that the roofing material must still be applied on the erected roof and at the same cost as on the more conventional construction of sheathing applied to roofing structures. Currently, this amounts to about 15 to 18 cents per square foot for a three-ply roof built up of tar and roofing felt with no gravel surfacing.

Finishing the inside surface of prefabricated panels with paint also presents a problem in that it adds to the final costs of the installed panel.

This invention comprises a wooden composite structural building panel made up of a lumber center and wood veneer or lumber crossbands and may include hardboard or wood surface facing layers. The invention also 3234374 Patented Feb. 8, 1966 includes the process of producing said composite structural panel.

The center is made up of longitudinal lumber strips of varying widths. The lumber strips are cross-banded with veneer or lumber bonded to each flat surface of the strips. Hardboard or veneer surfaces may in turn be bonded to the crossband.

The edges of the lumber strips are routed to provide a concave surface. In this way the strips are edge butted to the extent that contact between strips is made only in the area immediately proximate to the fiat, generally parallel top and bottom surfaces. A void is left between any two abutting strips along the entire length thereof. In this way expanding or swelling of the wood strips by virtue of moisture absorption enables the wood to expand with a minimum of stressing either of the crossband or the surface layers. The edge butting of the lumber strips provides a continuous, flat surface under the crossbanding and thus minimizes surface concavities and telegraphing defects when veneer crossbanding is used. Such defects are frequently encountered in conventional, spaced, lumber-core panels due to non-continuous support beneath the surface layers. Thus there is inherent in the design of this composite wooden panel a dimension stabilizing feature, the advantage of which will become apparent in subsequent discussion.

Accordingly, it is an object of this invention to provide a composite wooden panel which is extremely simple in design, rugged and strong in construction, and economical to produce.

Another object of this invention is to furnish a prefabricated structural panel which inherently possesses a high degree of fire endurance because the primary structural component, the core, which is preferably lumber, is protected from charring by one or more face components.

Another object of this invention is to furnish a prefabricated structural panel which may be made fire retardant in portions of its construction or in the entire panel itself.

Another object of this invention is to supply a prefabricated structural panel which permits the use of low grade lumber for the center without any impairment of its structural characteristics.

A further object of the invention is to provide a prefabricated panel having a minimum of surface defects caused by spaced core members.

Still another object of this invention is to provide a prefabricated structural panel which because of its low cost and design permits factory finishing of those surfaces of the panel which will be exposed on the inside of the building.

Yet another object of this invention is to furnish a prefabricated structural building panel which has inherent dimensional stability even in the face of considerable moisture absorption.

A further object of this invention is to provide a prefabricated structural building panel which even though it is made up of a number of edge butted center strips forces the individual center strips to work structurally as a unit.

These, together with other objects and advantages which will become subsequently apparent, reside in the details of construction and operation and method of making as more fully hereinafter described and claimed, reference being had to the accompanying drawings, forming a part thereof, wherein like numerals refer to like parts throughout, and in which:

FIGURE 1 is a partial view in perspective of the structure of this panel;

FIGURE 2 is a partial view in perspective showing that the facing or outside layers may be a wood veneer as well asthe hardboardfacing or outside layers as shown in FIGURE 1;

FIGURE 3 is a partial view in perspective showing that the crossbanding may consist of random Width lumber pieces arranged with their grain at an angle to the center lumber strips; I

, FIGURE 4 is a partial perspective view showing an alternative form of void space between pairs of center" the void need not take any specific form.

When the strips 12 are edge butted, an air space or void is created along the entire length of the abutting. strips. The function of the edge butted lumber strips 12 is; to

provide strength'and stiffness to the panel as well as in The mass of the sulation qualities and fire endurance. lumber itself would enable the panel to qualify as heavy mill construction under conventional building codes;

It is preferable that the lumber strips be cut so that their longitudinal dimensions coincide withtheir wood grain direction. The desired grain direction ofthe lumber strips is shown in the drawings by'arrow 16. It is also preferred, but not essential, that the grain of-the lumber strips be oriented as nearly as possible in a direction normal tothe crossband surfaces 22. Such preferred direction of the grain'is shown by the arrow 18. Such orienting of the wood grain ispreferred because when wood becomes moist it expands primarily in a direction normal to the grain pattern. the arrow 18, expansion of strips12 would tend to narrow the space between the surfaces 14.

The structural center strips 12 may be made of low grade, light weight wood species such as lodgepole pine,

western red cedar, spruce, fir and others with which those skilled in theart will be familiar. The precise dimensions of the lumber strips 12 will depend upon the distances which the panels may be required to span and the anticipated loads on the panel. For an eight foot span, a

center section approximately 2 inches thick, made up of Such a panel, made of west coast strips 12, is-desirable. Douglas fir, will carry design loads of forty pounds per square foot with a deflection of approximately 0.4 inch.

Preferably the strips-are kept narrow (i.e., less than 6" wide) to produce the optimum quality panel having the desirable qualifications mentioned previously. The thickness required in the panel is a function of the inherent 1 stiffness of the particular lumber center pieces being used.

Since the stiffness of the lumber is essentially independent of grade the center of the. panel could be made most The strips 12 make .up the Thus, referring again to ,20 the configuration of the recessed side faces which define strength whichmust be designed into the panel. The. crossbands also serve the veryimportant functions of stabilizing the panel against dimensional change and affording surface continnity for the lumber strips. Since wood does not appreciably shrink or swell along the grain the crossbands are placed with their grain running. at an angle, and in the preferred embodiment such angle would F be substantially-1a right-angle to the grain of the lumber strips. center or strips 12 to shrinkiand swelliacro'ss' their grain. Finally, outside layers may be added to the cross bands to'further strengthen thepanelstrncture and to provide .faces on both: sides that are capable of-beings appropriately finished. Preferably the faces referred to The crossbandsthitsrestrain the tendency of the by number 24 are a hardboard material such as aresin bonded wood fiber. materiaLi The faces 24; in'. the pre ferred embodiment are approximately of-an inch thick in their finished state.

Hardboard has beenfound to be particularly suitable as a facing because it is dense, absorptive, of uniform;

texture, and yet strong.

It reinforces the basic center and core structure but by the same token the hardboard face itself is'restrained against dimensional change by both the center and the cores.. The hardboard provides an excel- 1 lent base for factory treatment with roof or floor coatings,

paints and other finishes.- The density of the facings 24 in hardboard form giv'es them'inherently more resistance. to fire, ,;even without fire retardant treatment than lowerv density veneer faces.

Whiletas has been mentioned, the structural panel of this invention because of the hardboard facings has excellent resistance .to :fi're, nevertheless if greater :fire resist-g ance :is desired each or all of the component parts can be separately treated with fire retardant compositions before assembly It is not desired to limit this invention to a panel which has only a hardboard facing. As shown in FIGURE Z ther facing ;could:be made of veneer. In this case the facings 26 must be bondedto .the outside; surfaces of the economically of strips of lumber of very low grade and value, with attendant cost savings.

A crossband is bonded to the opposed flat surfaces of the lumber strips 12 with the strips arranged in-sideby-side or edge butted relationship. Such crossbands may be made of sliced or rotary cut veneers as shown in FIGURES l, 2 and 4, or may be made of random width The crossbands, 20 or-20a are placed so that the grain thereof, as indicated sawn lumber as showninFIGU'RE 3.

by arrow 22, runs at an angle, normally a rightangle, to

the grain of strips 12. The; crossbands act as a-load i equalizer forcing the individual strips to Work structurally as a unit. The crossbands 20 are in the preferred embodiment approximately /8 inch thickbut can-vary from this value depending m me type of crossbanding and crossbands 20 \Wlth the grain at an angle to the grain of theicrossband. Thus, in effect, the grain of'the faces 26 would be running in the same directiontas the. grain in the. strips 12.

The panels are preferably fabricatedin a1single pressing operation. When facedpanels are. made, the face material (hardboard unconsolidated resin-bearing fibrous mats, or woodveneer) is first placedon a suitable :sup-

porting surface.- Next, the .crossband is coated on bothv sides with a. suitable :adhesive andplaced on the face sheet. The flat surfaces of the lumber strips 12 are then placed on :the adhesive coated surface of-the crossbands,

oriented as previously described." It is 'essentialthat the.

strips be placed in edge-butting relationship to one :another.v A second adhesive coated crossband iszthen placed onithe strips and the, second face material placed on the crossband.

The assembly .is. next placed in a suitable press andv consolidated under pressure.-

During the :pressing the adhesive which .bonds thernembers is setsto form the.

composite panel.

If icold setting'adh'esi'ves are used, the pressing operation must-be continued until the .adhesiveis sufficiently' strong to hold the components togethen The panels canbe removed from the'press before the. adhesive is fully:

cured if they are handled carefully in accordance with standard cold press plywood manufacturing techniques.

Alternatively, 'restrainingt clamps may beemployed to provide'continuous pressureuntil theadhesive isi fully set.

If thermosetting adhesivesare used, such asthose based onssynthetic resins, (the assemblygmust be heated while;

under pressure .to a temperature and for. a time suflicient to set the adhesive- The panel may be bonded with !a variety of: adhesives; Thus, adhesives based on casein, animal blood, soya meal,

syntheic resins, or various combinations of the same, are usable. In general, any recognized wood adhesive has been found to be acceptable. The exact type of adhesive used will in general depend on the type of bond desired. Wet adhesive may be applied to the cross band by roller coating, spraying, brushing, or any combination of these methods. Dry film adhesives, comprising paper impregnated with resins and subsequently dried, may also be used. Fast curing, wet film adhesives such as those disclosed inco-pending US. application Ser. No. 37,513 filed June 20, 1960, may also'be used.

The faces 24 or 26 can be bonded to the crossbands in the same pressing operation in which the crossbands are banded to the lumber strips 12, or they may be bonded to the crossbands inn-secondary pressing operation.

Faces 24 can also be formed and simultaneously bonded to the crossbands by employing the process of copending US. patent application Ser. No. 96,923, filed March 20', 1961. In this case, the facing would actually be formed and consolidated to a hard surface. in the same pressing'operation which structurally unites theparts of the panel. In this instance, hot pressing must be emplayed.

The panels can be fabricatedzin standard 6 /2, 8 or 10 foot lengths by 2, 3 or 4 foot widths. In an alternative method of assembly the lumber strips 12 can be edge butted and held together temporarily by a restraining device until the crossband and adhesive can be placed on the opposed fiat surfaces.

The form of longitudinal void between the edge butted strips may vary. FIGURE 4, is illustrative of atype which has been found to be useful in that the strips may be edge glued at the contacting surfaces 30 prior to placirig the crossbands in position against the flat surfaces of the strips. Edge gluing the individual strips together facilitates handling as a unit and is readily adapted to machine assembly methods.

Itis desirable for best results that the crossband 20 have about 3 to 6 percent moisture content, although the exact'mois'ture content should be the optimum for the type of adhesive employed.

To avoid the tendency toward differential thickness shrinkage in the lumbercenter strips 12, careful control of moisture content of the lumber center strips is necessary. A 6 to 12 percent moisture content is generally optimum for gluing. However, a moisture content below 6% and above 12% can usually be tolerated by making suitable adjustment in the adhesive.

FIGURES represents an alternative embodiment of this invention in which the lumber strips 32 are separated from each other by a center strip made of plywood and in which the crossbanding is also made of plywood. It will be noted that the center lumber strips 32 are orientedas in other embodiments with the longitudinal dimension cut with the grain direction as shown by arrow 38. Similarly the end grain pattern of lumber strips 32 is as nearly practicable normal to the crossbanding surfaces as indicated by arrow 36.

The lumber strips 32 are, like the embodiments shown in FIGURES 1 through 4, provided with opposed recessed edge surfaces 34. The edge surfaces also have at the upper and lower margins thereof the contact or edge butting surfaces 40. Between each two lumber strips 32 is placed a plywood, preferably three-ply, center strip 42. Said center strips 42 are cut so that the grain direction of the outside surfaces extends in the same direction as that of the strips 32. As is well known to those skilled in the art the adjoining veneers of plywood are placed together so that the grain directions cross. Thus, the center veneer of strips 42 would extend generally normal to the crossbanding surfaces in a manner similar to strips 32 as indicated by arrows 46. The plywood crossbanding pieces 44 are also of conventional construction.

Thus the two outside veneers, as represented by arrows 48, have their grain directions running across, generally at a right angle to the grain direction of strips 32.

The plywood center strips are not recessed on any surface but are merely cut to the desired dimensions. The

recessed surfaces 34 in the lumber center strips 32 form elongated voids between each pair of center strips. The contact surfaces 40 abutting the plywood center strips result in the core or center of the panel having surface continuity for the crossbands. Obviously it is contemplated that the core design shown in FIGURE 5 could also have other types of crossband material, as for instance those shown in FIGURES l to 4. It is also apparent that the outer veneers of the plywood crossbands of FIGURE 5 could be finished or that a facing layer could. be added thereto.

The foregoing is considered as illustrative of the principles of this invention. Modifications and changes will occur to those skilled in the art but it is not intended to limit the invention to the exact construction, operation and process shown and described.

What is claimed is:

1. A composite wooden structural panel comprising:

a plurality of elongated wooden center strips of uniform thickness in side-by-side, edge-abutting relationship,

said center strips in cross-section having opposed recessed side edges and also having opposed substantially parallel and flat top and bottom surfaces so that an elongated air space is defined between any pair of abutting center strips and so that said top surfaces and said bottom surfaces, respectively, are in common planes,

said elongated air space in cross-section having its dimension normal to said top and bottom surfaces greater than its dimension parallel to said top and bottom surfaces,

said center strips being formed so that the grain thereof extends longitudinally,

a wood crossband bonded by'adhesives to each of said top and bottom surfaces, the grain. of said crossband extending generally across the grain of said center strips, and

the top and bottom portions of said center strips being in contacting relationship with each other for continuous support of said crossbanding material.

2. A composite wooden structural panel, comprising:

a plurality of elongated wooden center strips of uniform thickness in side-by-side, edge-abutting relationship,

said center strips in cross-section having opposed recessed side edges and also having opposed substantially flat and parallel top and bottom surfaces so that an elongated air space is defined between any pair of abutting center strips and so that said top surfaces and said bottom surfaces, respectively, are in common planes,

said elongated air space in cross-section having its dimension normal to said top and bottom surfaces greater than its dimension parallel to said top and bottom surfaces,

said abutting center strips contacting each other only in areas in close proximity to each of said top and bottom surfaces to form continuous support for a wood crossband bonded by adhesives to each of said top and bottom surfaces, the grain of said crossband extending generally across the grain of said center strips, and

a hardboard facing bonded by adhesives to said crossband to form a unitary structural panel assembly.

3. A composite wooden structural panel, comprising:

a plurality of elongated wooden center strips of uniform thickness in side-by-side, edge-abutting rela tionship,

said center strips having opposed substantially parallel,

top and bottom surfaces and in cross-section having opposed recessed side edges'so that an elongated air space is formed between any pair of abutting center strips, said elongated air space in cross-section having itsdi mension normal to said top and bottom surfaces greater than its dimension parallel to said ,top and bottom surfaces, said top surfaces and said bottom surfaces, respectively, being in common planes, with said center strips being cut so that the grain thereof extends form thickness inside-by-side, edge-abutting 'rela-.,

tionship, with .atleast every other one of said strips in cross-section having opposed recessed side edges defining contactsurfaces at the extreme .loWer and extreme upper margins of said edges,

all of said center strips having opposed substantially parallel 'top and bottom surfaces and said center strips being formed so thatthe grain thereof extends longitudinally,

said plurality of center strips forming an elongated airspace between any pair of said abutting center strips, 7

said elongated air space lllrCl'OSS-SfiCtlOl] having i'ts di-i mension normal to said top and bottom surfaces greater than its dimension parallel to said top and bottom surfaces,

wood crossbands bonded by adhesive to each of said it top and bottom surfaces, the grain of said cross I bands extending generally across the grain of said center strips, and

said contact surfaces being in contacting relationship with each other for continuous support of said crossbanding material. 4 5. A composite wooden structural panel, comprising: a plurality of elongated center strips of uniform thick:

ness in sideeby-side, edge-abutting relationship, with every other one of said center strips being made of lumber and being cut, so that the grainthereof extends longitudinally,

said plurality of said center strips having oppoesd substantially parallel top andbottom surfacesand said lumber center strips in cross-section having opposed between any pair, of abutting center strips, said elongated air space in;cross-section having its di- -mension normal to said itop and bottom surfaces greater; than its dir'nensionaparallel. to said top and bottom surfaces,

said top and bottom surfaces respectively being in commonplanes, withthe=center strips disposed between said, Ewoodlumber strips being of'iplywood construction and having :the grain of the outside veneer thereof extending :generally longitudinally,

wood cross bands bonded, by adhesives to each of saidtop'and bottom surfaces, the'grain of said 'crossbands extending (generally across the grain of said center strips, andsaid contact, surfaces being in contacting relationship with said iplywood construction center. strips for;-

continuous support of said crossbanding material. 6. A COIIIPOSltGwWOOdGH' structural panel, comprisingzi a plurality of'elongated wooden center strips, ofiunin form thickness invside-by-side; edge-abutting rela-v tionship,

said center strips in cross-section havin'g opposed re-y cessed side edges 'defininggcontact surfaces atzthe extreme .lower and extreme .upper margins. of said 1 surfaces, andalso having opposed substantially fiat and parallel ,top and bottom; surfaces so that an r,

elongated air space is definedbetween any pair of I abuttingcenter strips and so that saidtop surfaces;

and said bottom surfaces, respectively,'are in com- I mon planes,-

said elongated airspace in cross-section having its dimension normal to said top and bottonrzsurfa'ces greater than its dimension parallel to said-,top and bottom surfaces, 1 said center; strips being formediso .that the grain there-.

- of extendsllongitudinally,

said abutting center strips Ybeingrgliied to each other:

only at saidv contact. surfaces formingcontinuous support for a ,wood crossband bonded by adhesives to each of saidtop and bottom surfaces, the grain of said crossbandextending generally across the grain, of said .centerstrip;

References, Cited by the Examiner UNITED STATES PATENTS f ALEXANDER WYMAN, Primary Examiner.

recessed side edges defining contact surfacesatthei MQRRISJSUSSMAN; EARDMl-YBERGERT, extreme lower and the extreme upper margins. of

Examiners.

2,250,683 7/1941 Slechta 161 118-, 2,544,935 3/1951 Orner 20 91 XR'i 2,713,014 7/1955- Johnson 1 61-56 X 2,869,598 1/1959 L'oetscher. 156--300 2,965,529 12/1960 Bright 161-139 

1. A COMPOSITE WOODEN STRUCTURAL PANEL COMPRISING: A PLURALITY OF ELONGATED WOODEN CENTER STRIPS OF UNIFORM THICKNESS IN SIDE-BY-SIDE, EDGE-ABUTTING RELATIONSHIP, SAID CENTER STRIPS IN CROSS-SECTION HAVING OPOSED RECESSED SIDE EDGES AND ALSO HAVING OPPOSED SUBSTANTIALLY PARALLEL AND FLAT TOP AND BOTTOM SURFACES SO THAT AN ELONGATED AIR SPACE IS DEFINED BETWEEN ANY PAIR OF ABUTTING CENTER STRIPS AND SO THAT SAID TOP PAIR OF ABUTTING CENTER STRIPS AND SO THAT SAID TOP SURFACES AND SAID BOTTOM SURFACES, RESPECTIVELY, ARE IN COMMON PLANES, SAID ELONGATED AIR SPACE IN CROSS-SECTION HAVING ITS DIMENSION NORMAL TO SAID TOP AND BOTTOM SURFACES GREATER THAN ITS DIMENSION PARALLEL TO SAID TOP AND BOTTOM SURFACES, SAID CENTER STRIPS BEING FORMED SO THAT THE GRAIN THEREOF EXTENDS LONGITUDINALLY, A WOOD CROSSBAND BONDED BY ADHESIVES TO EACH OF SAID TOP AND BOTTOM SURFACES, THE GRAIN OF SAID CROSSBAND EXTENDING GENERALLY ACROSS THE GRAIN OF SAID CENTER STRIPS, AND THE TOP AND BOTTOM PORTIONS OF SAID CENTER STRIPS BEING IN CONTACTING RELATIONSHIP WITH EACH OTHER FOR CONTINUOUS SUPPORT OF SAID CROSSBANDING MATERIAL. 